A large continuous supply of relatively, homogeneous yeast strains are being obtained from hospitals in the form of clinical isolates of Candida albicans. These strains are being tested for levels of resistance to mercury cations, cadmium cations, silver cations, methyl mercury and phenyl mercuric acetate, both with discs (similar to those which are commercially available for antibiotic testing) and by replica platings (with a semi-automatic device, 20 strains at once) upon a series of plates with graded concentrations of the toxic substance. Those strains with higher than normal resistance to one or more compound of interest are being investigated further. In particular, the strains which are found to volatilize mercury cations are being investigated for the presence of plasmid (supercoiled) DNA, either in the mitochondria, cell nucleus or cell cytoplasm.